In general, as a method of generating ions in an ion source, for example, a method of generating the ions by causing discharge in gas has been known. In this case, a microwave or an electron beam may be used in order to cause the discharge.
Meanwhile, a technology that generates ions by using a laser is present. By an ion source (hereinafter, referred to as a laser ion source) that generates the ions by using the laser, a laser beam is focused and irradiated onto a target set in a vacuum chamber, an element contained the target is vaporized (ablated) and ionized by energy of the laser beam to generate plasmas, the ions contained in the plasmas are transported as the plasmas are, and the ions are accelerated while extracting an ion beam.
According to the laser ion source, the ions can be generated by irradiating the laser to the solid target and it is advantageous in generation of multi-charged ions.
The ions generated in the laser ion source have a vertical initial velocity to the solid target (a surface of the solid target to which the laser beam is irradiated). As a result, a transportation pipe having the same potential as a generation section of the ions is extended to a downstream part to transport the ions. Further, the ions generated in the laser ion source are transported to a downstream apparatus (for example, a linear accelerator, and the like) connected to the laser ion source.
However, in order to stabilize an ion generation condition in the laser ion source, states (surface roughness, a distance from a focusing lens, and the like) at a point (hereinafter, referred to as an irradiation point) on the target to which the laser beam is irradiated need to be the same at all times. However, a crater is generated on the target onto which the laser beam is focused and irradiated, by ablation which occurs by focusing and irradiating the laser beam. That is, since the states of the irradiation point are different from each other in the case where the laser beam is further irradiated to the point to which the laser beam is already irradiated, it is difficult to stably generate the ions.
As a result, in the laser ion source, when the laser beam is irradiated to the target, the target needs to move in order to avoid the point on the target to which the laser beam is already irradiated. In the case where the laser beam is irradiated onto all surfaces of the target (that is, in the case where all the surfaces of the target are used), the target set in the vacuum chamber needs to be exchanged.
In the aforementioned laser ion source, vacuum needs to be released in order to exchange the target set in the vacuum chamber. In this case, a vacuum condition of the downstream apparatus connected to the laser ion source is also damaged and a lot of time is required to make a high vacuum state again. As a result, a maintenance time in the laser ion source is lengthened, which is not practical.